The present invention relates to implantable microphones, and more particularly to an implantable microphone usable with an implantable hearing aid system, or similar auditory prosthesis, that provides a significantly wider frequency response and improved signal-to-noise than has heretofore been achievable.
Cochlear implant technology allows those who are profoundly deaf to experience the sensation of sound. Current cochlear implant systems include both internal, or implanted, components and external, or non-implanted, components. Typically, the implanted components have comprised an implantable pulse generator (IPG) connected to a cochlear electrode array adapted to be inserted into the cochlea. The external components have typically comprised an external microphone connected to an external speech processor, and a headpiece connected to the speech processor. In operation, the external microphone senses airborne sound and converts it to an electrical signal. The speech processor amplifies the signal and processes it in accordance with a desired speech processing strategy. After processing, control signals, fashioned to be representative of the information contained within the sound sensed by the microphone, are coupled to the IPG through the headpiece, and the IPG responds to these control signals by applying electrical stimuli to selected electrodes on the electrode array. Such electrical stimuli are sensed by the auditory nerve and transferred to the brain as the perception of sound.
Representative cochlear implant systems are described, e.g., in U.S. Pat. Nos. 3,752,939; 4,357,497; 4,679,560; and 5,603,726; which patents are incorporated herein by reference.
A significant problem associated with a fully implantable system is the microphone component thereof. An implantable microphone must be able to sense airborne sound from a location within the body tissue where the microphone is implanted. Conventional microphones that are designed to operate in air are not suitable for this purpose. Representative approaches that have been proposed in the art for an implantable microphone are found, e.g., in U.S. Pat. Nos. 5,888,187; 6,093,144; 6,216,040; and 6,422,991, and in U.S. patent applications Ser. Nos. 09/514,100, filed Feb. 28, 2000; and 09/854,420, filed May 11, 2001 (both applications are assigned to the same assignee as the present application); all of which documents are incorporated herein by reference.
Prior approaches for realizing an implantable microphone for use with a fully implantable system lack the signal-to-noise ratio and frequency response needed to allow a user of such implantable microphone to sense sounds beyond very basic speech sounds in a quiet environment.
The present invention is directed to an implantable microphone assembly suitable for use with an implantable hearing prosthesis, such as a fully implantable cochlear stimulation system, wherein the implantable microphone assembly exhibits, among other features, a wide frequency response and a high signal-to-noise ratio.
An implantable microphone assembly made in accordance with the present invention includes a diaphragm mounted to an outside surface of an hermetically sealed case. The mounting is made, in one of various embodiments, by way of an hermetic weld around the circumference of the diaphragm. A gap is created on the underside of the diaphragm when the diaphragm is lifted with internal pressure. At least one radial acoustic channel is formed in the wall of the hermetic case to which the diaphragm is mounted. A first end of the channel opens into the gap at a location that is at or near the center of the underside of the diaphragm. A second end of the radial acoustic channel opens to the interior of the hermetic case at a location that is near the periphery of the diaphragm. An acoustic transducer is placed inside the hermetic case and coupled to the second end of the acoustic channel so as to sense variations in pressure that occur in the gap due to deflections of the diaphragm caused, e.g., by external sound pressure. The interior space inside of the hermetic case directly underneath the diaphragm may be used to house and mount other components, such as a battery. The interior of the hermetic case, which interior includes the gap and radial channel, is pressurized in order to lift the diaphragm to form the gap and enable the diaphragm to move in response to external sound pressure.